1. Field of the Invention
This invention relates to an aluminum oxide-coated tool member in which a coating layer of aluminum oxide excellent in peeling resistance is coated on a substrate of metal, an alloy or a ceramics sintered body whereby lifetime of the tool is elongated. More specifically, the present invention relates to an aluminum oxide-coated tool member in which an intermediate layer is interposed between the substrate of metal, an alloy or a ceramics sintered body and an aluminum oxide-coated layer in view of difference in thermal expansion and suitability at the interfaces, which is most suitable for cutting tools such as turning tools, milling tools, drills and end mills; shaping tools such as dies and punches; wear resistant tools such as cutting blades including slitter, and cutting blades; corrosion resistant and wear resistant tools such as nozzles and coating tools; tools for the civil engineering and construction industry represented by cutting tools, digging tools, drilling tools and pulverizing tools to be used for a mine, road and construction.
2. Prior Art
A coated member comprising a substrate of metal, an alloy or a ceramics sintered body, and a coated layer provided thereon which is harder than the support by using a chemical vapor deposition method (CVD method), a physical vapor deposition method (PVD method) or a plasma CVD method whereby synergistic effects of the strength and toughness of the substrate and wear resistance of the coated material are developed has heretofore been used in practical. At present, representative materials of the coated layer in the coated material which have been practically used may include a Ti element-containing coated layer such as a nitride, carbide or carbonitride of Ti, a composite nitride or a composite carbonitride of Ti and Al; and an aluminum oxide coated layer.
Among these coated members, a number of coated members in which a coated layer of aluminum oxide is coated on a substrate whereby characteristics of the aluminum oxide are effectively utilized whereby long life time is established has been proposed. When a coated member in which a coating layer of aluminum oxide is coated on a substrate is used as a tool, if it is used as a cutting tool used at a high temperature under severe conditions, an adhesiveness between the substrate and the aluminum oxide coating layer is to be improved. In Japanese Provisional Patent Publication No. 256503/1992, a material to solve the above problems has been disclosed. Also, as a prior art technique regarding an oxicarbide of Ti and Al which is not directly relevant to the issue of adhesiveness between the substrate and the coated layer of aluminum oxide, there may be mentioned J. Vac. Sci. Tech. A(4)6 1986, pp. 2707 to 2712.
Among the prior art techniques regarding aluminum oxide-coated tool member in which a coating layer of aluminum oxide is coated on a substrate, in Japanese Provisional Patent Publication No. 256503/1992, there is disclosed a cutting tip made of a surface-coated tungsten carbide-base hard alloy excellent in peeling resistance which comprises an inner layer composed of a single-phase layer or multi-layers of at least one Ti compound selected from a carbide, nitride, carbonitride and carbonitroxide of Ti, an intermediate layer and an outer layer of aluminum oxide are successively coated on the surface of a tungsten carbide-base hard alloy substrate, and the intermediate layer is a mixed layer of the inner layer and the outer layer.
The surface-coated cutting tip disclosed in said publication employs an intermediate layer comprising a mixed layer of the inner layer and the outer layer so that peeling caused by strain in difference between thermal expansions at the whole surfaces of the respective layers is relaxed. However, there is not so remarkable relaxing effects on strain due to difference in thermal expansion at the tip of the blade of the cutting tip, particularly at the minute surface area of the cutting blade and there remains a problem that suitability of the outer layer and the intermediate layer is not in optimum conditions. Also, in the surface-coated cutting tip disclosed in said reference, among the components of the intermediate layer, the portion comprising the components of the inner layer is inferior in adhesiveness to the outer layer so that there is a problem that not so much effects can be expected about the adhesiveness between the intermediate layer and the outer layer.
As a method for coating the intermediate layer, there is disclosed that "a zone time of the inner layer and a zone time of the outer layer are each made 30 seconds and these layers are alternatively formed repeatedly" in Examples of said reference. According to this method, a layer of the inner layer components and a layer of the outer layer components are alternatively laminated with extremely thin layers, and thus, there is a problem that an effect of a mixed layer in which inner layer components and outer layer components are present in admixture in one layer cannot be obtained. Moreover, according to the method disclosed in said reference, there are problems that film forming operations at the forming step of the coating layer becomes complex, and it is necessary to additionally install a device for effecting film formation.
In J. Vac. Sci. Tech. A(4)6 1986, pp. 2707 to 2712 mentioned as another prior art techniques, there is disclosed an example in which a coating layer of Ti.sub.w Al.sub.x O.sub.v C.sub.z is formed on a TiC film by the CVD method and an amount of Al in the coating layer is made 3 to 58% whereby the resulting tool is used as a cutting tool. In said prior art reference, comparison between wear resistance in cutting tests using the Ti.sub.w Al.sub.x O.sub.v C.sub.z -coated layer and the conventional TiC coated layer, TiC-Al.sub.2 O.sub.3 laminated layer, etc. have been done. However, this reference is silent about the relationship between the Ti.sub.w Al.sub.x O.sub.2 C.sub.z -coated layer and the Al.sub.2 O.sub.3 -coated layer.